Does that mean that if you're sober, driving under the speed limit, and otherwise obeying all traffic laws, that you can drive topless should the urge arise?

It may not seem fair in this age of gender equality, but if you're a man, you're probably in the clear no matter where you are. If you're a woman, however, you may want to think twice, especially when driving in certain states.

Indecent Exposure Charges Are Possible

In most states, indecent exposure laws typically only cover (or uncover, perhaps) displaying of one's genitals, and a woman's breasts are not genitals. But some states have enacted laws that particularly mention a woman's breasts.

For example, Utah's lewdness statute makes it a crime to show "the female breast below the top of the areola" in a public place. Though you could try to argue that your car is not a public place, you would still likely be cited for exposing yourself on a public roadway, and have to explain yourself in court.